Analysis Of Ultimate Strength And Residual Strength For Oil Tankers

The ultimate load bearing capacity of ship hull structure is an important index expressing the safety and reliability of the structure, and it was widely been paid much attention and concern. But because of variety of ship types, complexity of ship structure, and relationship to strongly non-linear factors of material and geometry, the calculation of ship hull's ultimate strength becomes a complicated mechanical problem. After many years of research work and development, there are several methods to calculate the ultimate strength of a ship. Among all these methods, the progressive method is easy in application, and accurate in results, so it is introduced in IACS Common Structural Rules for Oil Tankers.One the other hand, a ship in navigation may happen to accidents of grounding or collision. When a ship is damaged, the local strength and longitudinal strength are reduced rapidly. To avoid further damage of ship and subsequent pollution to environment, it is necessary to know and assess the residual strength of damaged ship. With consideration of the asymmetry of the cross section and the shift of ship if the ship damaged by the collision or grounding, choose the direction of total moment as the calculate coordinate, avoid the problem of inclined moment when confirm the neutral axis. In the way of progressive collapse mechanism through incremented curvature, the neutral axis of cross section will not only moved up and down but also shift, so it must meet two equation conditions: One is the cross section is divided into two parts, tensile part and compressive part, the total moment in these two parts must be equal. The other is the lines between the center of these two parts must along the direction of total ultimate moment.Based on the Common Structural Rules of oil tankers by IACS, a program is developed to calculate both the ultimate strength of intact ship and residual strength of damaged ship with consideration of the asymmetry of the cross section and the shift of ship. In this thesis, on one hand, the longitudinal ultimate strength of three steel boxlike models and four intact ships are calculated. The result is checked with some famous experts' results from International Ship & Offshore Structures Congress and experiment. The result is approving. On the other hand, the residual strength of four damaged ship was calculated, which was damaged in different position and extension by collision or grounding. The author plotted some cures and used the residual strength index and sensitivity analysis to reflect the influence of different damaged position, extension and transverse angle. Then conclusions are useful for making rules and assessing the residual ultimate strength of ships for succor or drag.